The present invention relates to a device for applying thin layers of powder or pulverulent material, particularly for applying successive layers in machines for a rapid prototyping.
The invention also relates to a process for laying down a layer with this device.
There is known from the patent application PCT FR 99/00357 a process for rapid prototyping by laser sintering, which permits obtaining ceramic pieces of complex shapes from a three-dimensional image, by sintering superposed layers of powder with the help of a laser.
Such a process requires the performance of steps of which one consists in spreading in the form of a thin layer the powder or mixture of powders and compacting this powder to increase its density.
The thickness of such layers is of the order of several tens to several hundreds of microns.
The means for forming the layers described above comprise a screed which permits transferring the powder contained in a first container toward the laser working zone with a suitable and constant thickness.
If such an arrangement produces satisfactory results during the use of most powders, there is a need to improve the formation of layers when the powders are more delicate to handle and above all when the granulometry of the powders decreases, when the ratio of the thickness of the layer and the granulometry varies, or else when the shape of the particles changes.
The document DE 4325573 describes a device for applying a layer of powder stored in a supply and spread on a support. This latter comprises screed means in the form of a slider that moves by jacks.
Also, at present, to permit the production of such layers, the powder is often selected as a function of needs, which is a constraint because it is necessary to crush precisely and classify the powders by classes of granulometry. Such an undertaking requires sophisticated means given the diameters of the grains.
Thus, to produce homogeneous layers, it is necessary to work with powders having a Theological behavior substantially identical to that of liquids, which is the case for example of atomized powders whose particles are substantially spherical and of a diameter of little variation.
Such a preparation is costly and above all leads to unacceptable requirements for industry.
When the powders used are of the flour type, which is to say they swell, it becomes very difficult or even impossible to produce homogeneous layers.
In the case of swelling powders, when the layers are less than 100 μm, the screed totally moves the powder, zonewise, which creates impermissible defects to produce quality finished pieces by rapid prototyping.
Such a problem arises in the use of rapid prototyping but it generally is present when it is desired to lay down thin layers of swelling powders.